Chimera states in coupled sine-circle map lattices

Systems of coupled oscillators have been seen to exhibit chimera states, i.e. states where the system splits into two groups where one group is phase locked and the other is phase randomized. In this work, we report the existence of chimera states in a system of two interacting populations of sine circle maps. This system also exhibits the clustered chimera behavior seen earlier in delay coupled systems. Rich spatio-temporal behavior is seen in different regimes of the phase diagram.We carry out a detailed analysis of the stability regimes and map out the phase diagram using numerical and analytic techniques.Comment: 10 pages, 5 picture

Dynamics of coupled Josephson junctions under the influence of applied fields

We investigate the effect of the phase difference of applied fields on the dynamics of mutually coupled Josephson junction. The system desynchronizes for any value of applied phase difference and the dynamics even changes from chaotic to periodic motion for some values of applied phase difference. We report that by keeping the value of phase difference as $\pi$, the system continues to be in periodic motion for a wide range of system parameter values which might be of great practical applications.Comment: 13 pages 13 figure

Phase effects on synchronization by dynamical relaying in delay-coupled systems

Synchronization in an array of mutually coupled systems with a finite time-delay in coupling is studied using Josephson junction as a model system. The sum of the transverse Lyapunov exponents is evaluated as a function of the parameters by linearizing the equation about the synchronization manifold. The dependence of synchronization on damping parameter, coupling constant and time-delay is studied numerically. The change in the dynamics of the system due to time-delay and phase difference between the applied fields is studied. The case where a small frequency detuning between the applied fields is also discussed.Comment: 14 pages, 8 figures, Accepted for publication in "CHAOS

Evaluation of a puzzle-based virtual platform for improving spatial visualization skills in engineering freshmen

Being able to spatially visualize and mentally rotate is a key skill necessary to succeed in graphics and subsequent engineering courses. Recent research has focused on methods to develop Spatial Visualization (SV) skills in engineering students, as it is a key skill to succeed in most of the STEM fields. However, in most of the engineering schools, the instructors find it very difficult to develop keen SV skills in students. The major factors contributing to this challenge include, but not limited to the huge class sizes, limited time to teach the material, lack of effective demonstrations and the unavailability of feasible hands-on activities. With the funding from the National Science Foundation, the authors are developing a puzzle-based active learning platform called Student Assistant for Visualization in Engineering (SAVE) for developing SV skills in engineering freshman. In the preliminary version of this learning platform, the students are asked to complete a quiz with tasks requiring SV skills. For any incorrect answer, they are provided with automated hints about their mistakes. These hints are expected to help them in solving the following tasks. If they commit three mistakes, the quiz locks itself and creates a report on their performance thus far. The students are able to go back and restart the quiz. The student\u27s target is to complete the quiz with a minimum number of attempts. In the study reported here, the effectiveness of this game platform in conveying essential concepts of engineering graphics is investigated. Firstly, SAVE is implemented in a smaller classroom and the student feedback is collected. Then, it is implemented in a freshmen graphics class in a large public university in the west coast. The performance of the participating students in a follow-up exam is compared against that of a control group. The results show that the use of SAVE improves students\u27 conceptual understanding compared to a control group, as measured by the scores in the follow-up exam

Large-scale unit commitment under uncertainty: an updated literature survey

The Unit Commitment problem in energy management aims at finding the optimal production schedule of a set of generation units, while meeting various system-wide constraints. It has always been a large-scale, non-convex, difficult problem, especially in view of the fact that, due to operational requirements, it has to be solved in an unreasonably small time for its size. Recently, growing renewable energy shares have strongly increased the level of uncertainty in the system, making the (ideal) Unit Commitment model a large-scale, non-convex and uncertain (stochastic, robust, chance-constrained) program. We provide a survey of the literature on methods for the Uncertain Unit Commitment problem, in all its variants. We start with a review of the main contributions on solution methods for the deterministic versions of the problem, focussing on those based on mathematical programming techniques that are more relevant for the uncertain versions of the problem. We then present and categorize the approaches to the latter, while providing entry points to the relevant literature on optimization under uncertainty. This is an updated version of the paper "Large-scale Unit Commitment under uncertainty: a literature survey" that appeared in 4OR 13(2), 115--171 (2015); this version has over 170 more citations, most of which appeared in the last three years, proving how fast the literature on uncertain Unit Commitment evolves, and therefore the interest in this subject

Studies on Chaos and Synchronization in ac-driven Josephson junctions

The main goal of this thesis is to study the dynamics of Josephson junction system in the presence of an external rf-biasing.A system of two chaotically synchronized Josephson junction is studied.The change in the dynamics of the system in the presence of at phase difference between the applied fields is considered. Control of chaos is very important from an application point of view. The role Of phase difference in controlling chaos is discussed.An array of three Josephson junctions iS studied for the effect of phase difference on chaos and synchronization and the argument is extended for a system of N Josephson junctions. In the presence of a phase difference between the external fields, the system exhibits periodic behavior with a definite phase relationship between all the three junctions.Itdeals with an array of three Josephson junctions with a time delay in the coupling term. It is observed that only the outer systems synchronize while the middle system remain uncorrelated with t-he other two. The effect of phase difference between the applied fields and time-delay on system dynamics and synchronization is also studied. We study the influence of an applied ac biasing on a serniannular Josephson junction. It is found the magnetic field along with the biasing induces creation and annihilation of fluxons in the junction. The I-V characteristics of the junction is studied by considering the surface loss term also in the model equation. The system is found to exhibit chaotic behavior in the presence of ac biasing.Department of Physics, Cochin University of Science and Technolog

Quantification of Fluorophore Copy Number from Intrinsic Fluctuations during Fluorescence Photobleaching

AbstractWe present a theoretical technique for quantifying the cellular copy-number of fluorophores that relies on the random nature of the photobleaching process. Our approach does not require single-molecule sensitivity, and therefore can be used with commonly used epifluorescence microscopes. Fluctuations arising from photobleaching can be used to estimate the proportionality between fluorescence intensity and copy-number, which can then be used with subsequent intensity measurements to estimate copy-number. We calculate the statistical errors of our approach and verify them with stochastic simulations. By using fluctuations over the entire photobleaching process, we obtain significantly smaller errors than previous approaches that have used fluctuations arising from cytoplasmic proteins partitioning during cellular division. From the time-dependence of the fluctuations as photobleaching proceeds, we can discriminate between desired photobleach fluctuations and background noise or photon shot noise. Our approach does not require cellular division and the photobleaching rate sets a timescale that is adjustable with respect to cellular processes. We hope that our approach will now be applied experimentally